A horizontal structure study was made on deciduous forest plot, in Achotines Laboratory, Provincia de Los Santos, Panama Republic. In this study was mesure a rectangular plot of one hectarea and this was split in 10 subplot of the same size each one (10X100 m). All the trees with DAP ? 10 cm, then all the trees were mesure and identified. With this information was calculed the Importance Valor Indice (IVI) of each tree species. The trees wth most IVI value were madroño (Calycophyllum candidissimum) with 34.04, then zorro (Astronium graveolens) with 32.48, nisperillo (Pouteria Campechiana) with 32.04, roble de sabana (Tabebuia rosea) with 29. 36, guayacán (Tabebuia guayacan) with 25.09 and cedro amargo (Cedrela odorta) with 20.06. The most important tree species is Calycophyllum candidissimum, because is the most abundant and frequent in the plot.